Recently, various schemes based on inter-cell interference control have been proposed to enhance throughput of the system and a user equipment placed at a cell edge. 3GPP and IEEE also deal with Inter-Cell Interference Coordination (ICIC), Fractional Frequency Reuse (FFR), Coordinated Multiple Point (COMP) and the like.
FIG. 1 illustrates a cell including a plurality of Radio Remote Heads (RRHs) according to the related art. In the present disclosure, it is assumed that a plurality of RRHs are present in each cell. In this environment, multiple RRHs belonging to one cell utilize the same cell ID and a user equipment may recognize these multiple RRHs as a single cell. Hence, although the user equipment moves between RRHs in a cell, handover is not incurred.
In addition, it is possible to enhance system throughput by use of spatial multiplexing wherein user equipments close to one RRH utilize the same frequency resources at the same time. It is also possible to enhance reception quality of a user equipment placed in the boundary between RRHs by transmitting the same data from multiple nearby RRHs or preventing RRHs other than RRHs transmitting data from using the corresponding resources.
To this end, it should be possible to measure channel quality between each RRH and the user equipment. However, as the user equipment cannot distinguish RRHs on the basis of downlink signals sent by the RRHs, it is not possible to measure channel quality using a downlink signal. On the other hand, it is possible for an RRH to measure channel quality between the RRH and user equipment using an uplink signal sent by the user equipment.
The uplink channel may be generally divided into a signal channel and a traffic channel. The signal channel indicates a channel that includes only physical-layer information without information related to the Medium Access Control (MAC) layer or higher. In the case of 3GPP Long Term Evolution (LTE), the sounding reference signal (SRS) and demodulation reference signal (DMRS) correspond to the signal channel. On the other hand, the traffic channel includes information related to the MAC layer or higher. In the case of 3GPP LTE, the PUCCH and PUSCH correspond to the traffic channel. In general, for detection of a signal sent by a user equipment in a neighbor cell, utilization of the signal channel transmitting physical-layer information only has an advantage over utilization of the traffic channel.
To support control of RRH-unit interference between RRHs indifferent cells (not using the same resources or transmitting the same data), it should be possible to measure a signal sent by a user equipment in a neighbor cell. However, in the related art, as each base station (eNB) independently operates the uplink signal channel, a signal sent by a user equipment in a neighbor cell is not measured and information needed for measurement is not exchanged.